1. Technical Field of the Invention
The present invention relates to an electronic memory device, for example, a magnetic memory device such as a hard disk drive device and the like, or an optical memory device such as a compact disk drive device and the like. More particularly, the present invention relates to a method of forming a protruded shaft which is used for installing various components or supporting rotational members or the like on a metal base of the electronic memory device.
2. Description of Related Art
A conventional electronic memory device, e.g., a hard disk drive (referred to as HDD) device is shown in FIG. 8(A). The HDD device is comprised of an approximately dish-shaped base 100 made of a metal plate and various kinds of members equipped in a recessed portion of the base 100 having an open upper face. The open upper face of the base 100 is covered with a plate-shaped top cover 101 and, as a whole, the electronic memory device is constituted of a roughly card shape.
Furthermore, the recessed portion of the base 100 is equipped with a magnetic disk as an information recording medium and various mechanisms such as a spindle motor for supporting and rotating the magnetic disk, a plurality of magnetic heads for writing or reading information from the magnetic disk, a head actuator 102 for movably supporting the magnetic heads with respect to the magnetic disk, a voice coil motor for swinging and positioning the head actuator, and a circuit board unit.
On activation of the voice coil motor, the head actuator 102 swings between an operating position on the magnetic disk and a retreated position. A stopper pin 103 formed of a protruded shaft is arranged on the base 100 to prevent an excess of swing movement over the retreated position.
A seal 104 made of rubber or the like is sandwiched between the edge portions of the base 100 and the top cover 101 so that the interior of the HDD device can be kept in an airtight condition. That is, the seal rubber is tightly interposed between the edge portions in the vertical direction so that the interior of the base 100 is protected from entering dust from the outside. This is because the contamination such as minute dust suspended in the outside air or the harmful ion causes the error due to attaching on the surface of the magnetic disk.
In the conventional HDD device, the stopper pin 103 is formed as shown in FIGS. 8(A) or 8(B). A stopper pin 103 in FIG. 8(A) is integrally protruded inside of the base 100 made of a metal plate. The metal base 100 is placed on a die (not illustrated) provided with a hole having a predetermined inner diameter and performed a burring processing from the back side of the base 100 to form the protruded cylindrical-shaped stopper pin 103 which is formed a through hole. A stopper pin 103 shown in FIG. 8(B) is constituted in such a manner that a through hole is formed in the base 100 and the stopper pin 103 made of a shaft member is separately fitted into the through hole. Then the stopper pin 103 is crimped to the base 100. The stopper pin may be fixed to the base by a screw.
As described above, the conventional stopper pin 103 is formed of a cylinder, which is penetrated in the vertical direction as shown in FIG. 8(A). Therefore, the interior of the HDD device communicates with the outside. As a result, there may be a problem that foreign particles called contaminant such as minute dust or harmful ion enter into the interior of the HDD device from the outside and causes an error due to the attaching of the particles to the surface of the magnetic disk. In order to prevent the above problem, it has been known a means for sealing the interior of the HDD device from the outside with a sealant 105 inserted into the hollow part of the stopper pin 103. It has been also known a means for sealing the interior from the outside with a sealing tape stuck to the bottom surface of the base 100. However, the means of inserting the sealant 105 generates a harmful gas from the sealant 105 and it may cause the surface of the magnetic disk to change in quality.
Moreover, according to the method of crimping the stopper pin 103 to the base 100, there may be a problem that a required strength can not be obtained since the thickness of the base 100 becomes thinner as the height of the HDD device has been reduced. Another method is that a through hole is formed in the base 100 and then a stopper pin 103 is fixed to the through hole by a screw. However, this method increases necessary parts and working steps and thus inevitably results in the increase of manufacturing cost.